1. Field of the Invention
The present invention relates to an image processing method for efficiently printing out image data for spot color printing by use of an image forming apparatus which is not compatible with the spot color printing.
2. Description of the Related Art
In recent years, digital printing techniques have steadily been increasing their utility values in markets, such as an on-demand printing market and a small-lot document printing market. Particularly, full-color printing using an electrophotographic technique is in a superior position to other printing techniques in light of productivity, printing costs, easy maintenance, and so forth and is therefore rapidly expanding the market. In terms of such color printing, attention is drawn to not only conventional full-color printing according to electrophotographic printing that uses four color toners of C (cyan), M (magenta), Y (yellow), and K (black) but also multiple-color printing methods using an additional special toner. Accordingly, these multiple-color printing techniques are now with an eye toward a market of special printing that highly requires on-demand and immediate printing performance. Such special toners include, for example, a transparent toner which is capable of absorbing irregularities on a surface of a printed sheet and achieving high glossiness, and a light toner which is capable of reducing roughness of a highlighted part. By using the special toners, it is possible to gain new added-values that are different from what is obtainable by normal digital printing, and hence to further expand the world of digital printing. From the above-described background, image forming apparatuses which are generally called multifunction printers (hereinafter referred to as “MFPs”) and equipped with special toners are now being brought to the market in addition to conventional color MFPs configured to perform conventional four-color printing.
Moreover, for effectively using special toners, a large number of application software products capable of handling a spot color other than C, M, Y, and K are being brought to the market. It is possible to generate image data containing the spot color by using such application products.
Although image data containing a spot color has started to be used as described above, it is not always true that every MFP used today is compatible with the spot color. Specifically, it is highly likely that a print job is sent to a network which includes both of an MFP compatible with a spot color toner and an incompatible MFP using the conventional four colors of C, M, Y, and K. This situation causes a problem of inefficiency in which an unnecessary rendering operation for a spot color is performed even when image data containing the spot color is to be printed out by an MFP which is not compatible with the spot color. To solve this problem, Japanese Patent Laid-Open No. 2008-028917 discloses a method of determining prior to printing whether or not to use a spot color, and then determining whether to perform rendering for the spot color or rendering for the conventional four colors according to the determination result.
In recent years, environments have been created in which image data stored in a storage component of a certain MFP can be printed out by using another MFP connected to the same network. Under such an environment, the technique described in Japanese Patent Laid-Open No. 2008-028917 cannot deal with a case where image data stored in a spot color compatible MFP that has performed spot color printing of the image data is to be printed by another MFP not compatible with spot color printing. This is because the image data stored in the storage component of the spot color compatible MFP has already been rendered for the spot color. Therefore, when a conventional four color MFP is designated as a printer for printing the image data already rendered for the spot color, a problem arises that the MFP is incapable of printing the image data properly. To be more precise, the MFP is incapable of printing the image data from the beginning, or incapable of reproducing proper colors in a part of the image data rendered for spot color even when the MFP prints out the image data by using the four colors only.